1) I saw "Rocky Horror" once, many moons ago, but I don't remember the music well enough to comment on it. I do remember the film well enough, though, to agree with your "so camp it is brilliant" comment.
2) "The Blues Brothers" -- Fantastic! Love it!
3) I haven't seen "Rock of Ages."
My personal favorite:
"The Umbrellas of Cherbourg," a classic 1964 romantic French film directed by Jacques Demy and starring Catherine Deneuve, in which every word is sung rather than spoken. The music having been composed by Michel Legrand.
Dewey Cox story, okay raunchy and not appropriate for watching with kids but the paraody of Johnny Cash, Bob Dylan, and Brian Wilson songs were fanatastic, songs like Walk Hard, Let's Duet, Midget Man just fanatastic.
Rocky Horror a Classic
Across the Universe great Beatles songs redone
The Who's Tommy some great songs and of course a 40 ish Ann Margret
Chicago great songs, great music, great dancing, hot women
West Side Story - is this the best ever score? Probably. Oliver! - Lionel Bart, what more do you want? My Fair Lady - timeless songs Once Upon a Time in the West - epic score Harold and Maude - Cat Stevens circa 1970
"The Wall". It most strictly meets the original question as a Music Movie. The music itself stands on its own as it was developed first and contains very little dialog. It artistically mixes animation and live action and is enjoyable with eyes opened or closed. The songs are meaningful and the movie is not filled with non-singing twittering about breakfast or a contrived transition to bridge memorable songs.
To me, "Tommy" contains too many elements of a musical and is better contexted as a true rock opera but not as cohesive when considered as stand-alone music. There are far too many plot transition jingles/songs that only maintain their relevance in the context of the film....Tina Turner's Acid Queen and the injured glamour girl with the child Frankenstein guitarist on stage...as examples.
"Yellow Submarine" should not count but it is simply brilliant and a very stark contrast to the other
movies which were more simply live documentaries masking their early explorations in drugs and religion...and drugs. If only the world had more studio footage of the Beatles in action.
"West Side Story", "Grease" and even "The Rocky Horror Picture Show" were adaptations of musicals as well as "Sound of Music". "Little Shop of Horrors" was well done also if you like that sort of thing, but still originally musicals.
"Spinal Tap" and "A Mighty Wind" are great musical mockumentaries.
"The Last Waltz" has Scorsese's involvement and reached a wider audience for that reason and the very special guests, but would not consider it a "movie".
"Frozen" and "Tarzan" (moreso Tarzan) have good soundtracks but so did "Snow White" and "Mary Poppins".
If your talking about sound quality,nothing is close to the new Queen Movie. Not in my opinion. Sounds like a concert in 5.2. I actually bought a 4K version just as a "show off your system " . It's mixed as well as some of my video concerts.